Electron beam measurement apparatus

ABSTRACT

The present invention provides an electron beam measurement technique for measuring the shapes or sizes of portions of patterns on a sample, or detecting a defect or the like. An electron beam measurement apparatus has a unit for irradiating the patterns delineated on a substrate by a multi-exposure method, and classifying the patterns in an acquired image into multiple groups according to an exposure history record. The exposure history record is obtained based on brightness of the patterns and a difference between white bands of the patterns.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2007-315940, filed on Dec. 6, 2007, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an electron beam measurement techniquefor measuring the shapes or sizes of portions of patterns on a sample,or detecting a defect or the like.

In recent years, a semiconductor element has been miniaturized, anddimensional control with high accuracy has been demanded. With theminiaturization of the semiconductor element, the wavelength of lightused in a lithographic process has been reduced. In the most currentlyadvanced factory, an ArF excimer laser (having a wavelength of 193 nm)is used. In order to miniaturize the semiconductor element, an extremeultraviolet (EUV) lithography using light with a wavelength of 13 nm isconsidered as a candidate. However, since the wavelength of light usedin the EUV lithography is shorter by one digit or more than that of theArF excimer laser, there is a controversy whether or not it is possibleto smoothly switch to the EUV lithography. As an alternative solution, amulti-exposure scheme has been proposed.

As an example of the multi-exposure scheme, a process flow of a doublepatterning technique (refer to, for example, SEMICONDUCTOR InternationalWeb-version: http://www.sijapan.com/issue/2007/04/u3eqp3000001dd9m.html)is shown in FIGS. 1A to 1G. As shown in FIG. 1A, a substrate W has aprocessed layer TL, a hard mask layer HM and a first resist layer RL1.The hard mask layer HM is provided on the processed layer TL. The firstresist layer RL1 is provided on the hard mask layer HM.

In a first exposure, a first exposure pattern EP1 is delineated in thefirst resist layer RL1 by an exposure apparatus (as shown FIG. 1B) anddeveloped (as shown in FIG. 1C). Next, the hard mask layer HM is etchedsuch that the first pattern is transferred into the hard mask layer HMas shown in FIG. 1D.

Then, an antireflection film BARC is formed in order to perform a secondexposure. After that, a second resist layer RL2 is formed (as shown inFIG. 1E). The second exposure is performed by using an appropriatereticle in the same way as the first exposure such that a secondexposure pattern EP2 is delineated in the second resist layer RL2 (asshown in FIG. 1E) and developed (as shown in FIG. 1F). A portion of thesecond exposure pattern EP2 is located between portions of the firstexposure pattern EP1. This makes it possible to delineate a fine pattern(that cannot be delineated by a single exposure due to a lack ofresolution) in a single layer.

Next, the processed layer TL is etched using the second resist layerRL2, the antireflection film BARC, and the hard mask layer HM as masks.Then, the second resist layer RL 2 and the antireflection film BARC arepeeled off. A pattern of the processed layer TL is formed as shown inFIG. 1G. In this case, the hard mask layer HM is typically not removed.The wafer is inspected in this state (shown in FIG. 1G).

SUMMARY OF THE INVENTION

Conventionally, only a sample subjected to a single exposure is targetedin the case where an electron beam measurement apparatus measures thesizes of portions of patterns on the sample. That is, it has beenunclear how to measure a sample subjected to a multi-exposure scheme andhaving a pattern that includes portions having shapes different fromeach other in a vertical direction.

It is, therefore, an object of the present invention to provide atechnique which uses an electron beam to measure a sample manufacturedby a multi-exposure scheme.

To accomplish the object, it is effective to provide means forclassifying patterns in an image acquired by charged beam scanning intomultiple groups according to an exposure history record, based onbrightness of the patterns and a difference between white bands of thepatterns. In addition, it is preferable to provide means which uses animage processing parameter or a waveform processing parameter for eachof the groups, and measuring the size of a portion of a pattern, theposition of the contour of the pattern, or a relative positionalrelationship be conducted. In this case, the used parameter variesdepending on the group.

As the means for classifying the patterns into groups, it is effectiveto provide means for comparing an acquired image with a design database.As the means for measuring the size of a portion of a pattern or theposition of the contour of the pattern, a reference image or a referencewaveform may be used. It is also effective to provide means which usesconditions for image acquisition itself to acquire images that have thesame pattern and are different from each other, and processes theimages.

Representative configuration examples of the present invention aredescribed below.

(1) An electron beam measurement apparatus, which measures, based oninformation on an image, a pattern formed on a sample, comprising: anelectron optical system that uses a lens and a deflector to scan apredetermined observation region on a sample with an electron beamemitted from an electron source; a detector for detecting a chargedparticle secondarily generated from the sample by irradiation with theelectron beam; and means for forming an image based on the detectedcharged particle. The electron beam measurement apparatus includes meansfor classifying patterns, which are included in an image acquired by theirradiation with the electron beam on the patterns on the sample, intogroups according to an exposure history record. The exposure historyrecord is obtained based on brightness of the patterns included in theimage and a difference between shapes of white bands of the patterns.The patterns are delineated in a single layer present on a substrate bya multi-exposure method. Image processing or waveform processing ispreformed on each group, the processing varying depending on theclassified group.

(2) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein the patterns are classified into thegroups based on an image formed based on a secondary electron of thecharged particle and an image formed based on a reflective electron ofthe charged particle.

(3) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein the patterns are classified into thegroups according to the exposure history record by comparing theacquired image with a design database.

(4) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein the patterns are classified into thegroups such that a pattern having portion arranged alternately isincluded in one of the groups that is different from the other groupincluding the other pattern.

(5) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein an image processing parameter or anwaveform processing parameter is used for each of the classified groupsto obtain the size of a portion of the pattern included in the group orthe position of the contour of the portion of the pattern, the usedparameter varying depending on the group.

(6) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein a reference image or a reference waveformis used for each of the classified groups to obtain the size of aportion of the pattern included in the group or the position of thecontour of the portion of the pattern, the used reference image or theused reference waveform varying depending on the group.

(7) The electron beam measurement apparatus having the configurationdescribed in item (1), wherein information on a relative positionalrelationship between the classified groups is obtained.

(8) An electron beam measurement apparatus, which measures, based oninformation on an image, a pattern formed on a sample, comprising: anelectron optical system that uses a lens and a deflector to scan apredetermined observation region on a sample with an electron beamemitted from an electron source; a detector for detecting a chargedparticle secondarily generated from the sample by irradiation with theelectron beam; and means for forming an image based on the detectedcharged particle, the patterns being delineated in a single layerpresent on a substrate by a multi-exposure method. The electron beammeasurement apparatus including means for classifying the patterns inthe plurality of images into a plurality of groups according to anexposure history record by irradiating patterns present on the samplewith the electron beam to acquire a plurality of images respectivelyindicating regions that mostly overlap each other under respectiveconditions different from each other.

(9) The electron beam measurement apparatus having the configurationdescribed in item (8), wherein the multi-exposure method uses a doublepatterning technique.

(10) The electron beam measurement apparatus having the configurationdescribed in item (8), wherein the image formed based on the detectedcharged particle is a scanning electron microscope image.

According to the present invention, it is possible to realize anelectron beam measurement technique capable of measuring the shape orsize of a portion of a pattern delineated on a sample by amulti-exposure method or detecting a defect or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G are diagrams showing an example of a process flow of amulti-exposure method.

FIG. 2 is a diagram showing a basic configuration of an electron beammeasurement apparatus according to the present invention.

FIG. 3 is a flowchart showing a basic measurement according to thepresent invention.

FIG. 4 is a flowchart showing a measurement according to a firstembodiment of the present invention.

FIG. 5 is a flowchart showing a measurement according to a secondembodiment of the present invention.

FIG. 6 is a flowchart showing a measurement according to a thirdembodiment of the present invention.

FIG. 7 is a flowchart showing a measurement according to a fourthembodiment of the present invention.

FIG. 8 is a flowchart showing a measurement according to a fifthembodiment of the present invention.

FIG. 9 is a diagram showing an example of a scanning electron microscope(SEM) image.

FIG. 10A is a diagram showing a secondary electron image.

FIG. 10B is a diagram showing a reflective electron image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings.

First Embodiment

First, a basic configuration of an electron beam measurement apparatusaccording to the present invention will be described.

FIG. 2 is a diagram showing the basic configuration of the electron beammeasurement apparatus according to the present invention. The electronbeam measurement apparatus has an electron optical system 201, asecondary electron detector 208, a reflective electron detector 215, acomputing unit 209, a display unit 210, a storage unit 211, and anelectron optical system controller 212. The electron optical system 201uses a condenser lens 203, a deflector 204 and an objective lens 205 toirradiate a sample (wafer) 207 placed on a stage 206 with an electronbeam emitted by an electron gun 202 and scan the sample. The secondaryelectron detector 208 is adapted to detect the intensity of a chargedparticle (secondary electron) secondarily generated from the sample 207by the irradiation of the electron beam. The reflective electrondetector 215 is adapted to detect the intensity of a charged particle(reflective electron) secondarily generated from the sample 207 by theirradiation of the electron beam. The computing unit 209 is adapted toprocess the waveform of a signal obtained from the detected chargedparticle to calculate a characteristic value. The display unit 210displays, through an input performed by an operator, a scanning electronmicroscope (SEM) image. The storage unit 211 stores data. The electronoptical system controller 212 reflects a condition for the irradiationwith the electron beam to the electron optical system to control theelectron optical system.

It should be noted that reference numeral 213 shown in FIG. 2 denotesflow of data (e.g., flow of a computed result) to be stored in thestorage unit 211, and reference numeral 214 shown in FIG. 2 denotes flowof data read out from the storage unit 211.

FIG. 3 is a flowchart showing a basic measurement according to thepresent invention. First, coordinates of an area to be measured areacquired in step 301. The scanning electron microscope (SEM) image ofthe region located at the coordinates is acquired by means of asecondary electron in step 302. Data on the acquired image is stored inthe storage unit 211 in step 303. Patterns within the acquired image areclassified into two groups (group 1 and group 2) in accordance with apredetermined rule in step 303. The size of a portion of a pattern ofeach group is calculated in accordance with a predetermined algorithm insteps 305 and 306.

It can be determined whether or not each exposure process is properlyperformed by determining whether or not each calculated size is in apredetermined range. If there is a group including a pattern having aportion of which the size is not in a predetermined range, a processcondition for a corresponding exposure process is reviewed. In theabovementioned way, it is possible to control processes of amulti-exposure method according to the present invention.

The present embodiment will be described with reference to FIG. 4.

In the present embodiment, an SEM image of the sample in the state shownin FIG. 1G is acquired. FIG. 9 is a schematic diagram showing the SEMimage. A pattern shown in FIG. 9 is part of a flash memory pattern. Aportion of the pattern shown in FIG. 9, which corresponds to a portion(at which the hard mask layer HM remains after a first exposure) of thesample, has higher contrast with the substrate than that of a portion ofthe pattern shown in FIG. 9, which corresponds to a portion (at whichthe hard mask layer HM does not remain and the processed layer remainsafter a second exposure) of the sample.

As an example of the classification method shown in FIG. 3, it ispossible to classify patterns into two patterns: a pattern delineated bythe first exposure; and a pattern delineated by the second exposure, inaccordance with brightness of the patterns (in step 401). When thepattern includes a defect, it is possible to easily determine whichexposure process has a problem.

In addition, the algorithm for calculating the size of a portion of thepattern can be changed to another algorithm for calculating the size ofthe portion. An SEM image of a certain portion (of the pattern) isviewed differently from an SEM image of another portion (of the pattern)having a height different from that of the certain portion and havingother dimensions that are the same as those of the certain portion. Itis therefore necessary to change the algorithm based on the portion ofthe pattern in order to optimally measure the portion. In the presentembodiment, the size of the portion of the pattern is calculated basedon coordinates of an intersection of a signal waveform and a slicelevel. A slice level for the hard mask layer HM is high, while a slicelevel for the processed layer TL is low. It is possible to set aplurality of slice levels in the electron beam measurement apparatusaccording to the present embodiment.

In the present embodiment, dimensional control is carried out by usingthe average of widths of a plurality of lines formed in each layer asthe size of a portion of the pattern. However, the dimensional controlmay be carried out by using the width of one line located at a centralportion of each layer.

In order to classify patterns into groups, it is effective to use adifference between white bands. The white bands are waveforms of signalscoming from edge portions of the patterns when an SEM performsirradiation with an electron beam. In addition, reference waveforms maybe used to calculate the sizes of pattern portions.

In a conventional technique, a measurement error between a firstexposure layer and a second exposure layer is 3 nm. According to thepresent invention, however, a measurement error between exposed layersis 0.2 nm. In addition, although a reproducible error in theconventional technique is 0.6 nm, a reproducible error in the presentinvention is 0.3 nm.

Second Embodiment

FIG. 5 is a flowchart of the measurement according to a secondembodiment of the present invention. In the measurement shown in FIG. 5,after an SEM image is acquired, patterns are classified into groups bycomparing the SEM image with design data, in step 501. In the pattern(shown in FIG. 9) having lines and spaces which are alternatelyarranged, matching of the pattern may be performed with a single pitchshifted. This measurement method shown in FIG. 5 is suitable for a logicLSI having a complex pattern. It can be considered that a combination ofthis measurement method shown in FIG. 5 with the classification methodbased on the brightness in the first embodiment is effective.

According to the present embodiment, the contour of a portion of eachpattern is detected, and the length of the contour is evaluated, toinspect a hot spot (which is a location at which a defect is likely tooccur). As a result, detection sensitivity can be improved in thepresent embodiment, compared with the conventional technique.

Third Embodiment

FIG. 6 is a flowchart showing a measurement according to a thirdembodiment of the present invention. In the present embodiment, aplurality of images is used. After the sample is moved to a locationdefined by coordinates of an area to be imaged, a single SEM image isacquired under a first condition in step 601, and a single SEM image isacquired in step 602 under a second condition different from the firstcondition. Under the first condition, the number of times of scanning ofan observation area is eight. Under the second condition, the number oftimes of television scanning of the observation area is 32. The reasonfor acquiring the images under the conditions different from each otheris that the intensity of a signal coming from the processed layer islow. Thus, the number of times of the scanning under the secondcondition is 32 in order to improve a signal-to-noise ratio. Theintensity of a signal coming from the hard mask layer is too high whenthe image acquisition is performed under the second condition. Thus, adetected signal is saturated.

After the patterns are classified, the size of the hard mask layer isobtained based on the image acquired under the first condition, and thesize of the processed layer is obtained based on the image acquiredunder the second condition. As a result, a reproducible error is reducedto 0.25 nm.

Fourth Embodiment

FIG. 7 is a flowchart showing a measurement according to a fourthembodiment of the present invention. In the fourth embodiment, aplurality of images is used. The sample shown in FIG. 1F is used only inthe fourth embodiment. After the sample is moved to a location definedby acquired coordinates of an area to be measured, a single SEM image isacquired by using a secondary electron in step 701 and a single SEMimage is acquired by using a reflective electron in step 702. The secondresist layer RL 2 shown in FIG. 1F can be easily observed. It is noteasy to observe the hard mask layer HM since the hard mask layer HM iscovered with the antireflection film BARC.

In order to observe the hard mask layer HM, a reflective electron isused. This results from the fact that the escape depth (to allow thereflective electron to escape from the sample) of the reflectiveelectron is large. FIGS. 10A and 10B are diagrams showing the image(secondary electron image) acquired by using the secondary electron andthe image (reflective electron image) acquired by using the reflectiveelectron image, respectively. In the secondary electron image shown inFIG. 10A, an image of the second resist layer RL2 is observed. In thereflective electron image shown in FIG. 10B, an image of the secondresist layer RL2 and an image of the hard mask layer HM are observed. Inthis method, the two images can be acquired simultaneously. Thethroughput of the electron beam measurement apparatus is therefore notreduced. In addition, it is easy to classify the patterns into groupsbased on the two images. The size of the second resist layer RL2 isobtained by using the second electron image having high contrast, whilethe size of the hard mask layer HM is obtained by using the reflectiveelectron image having contrast.

As a result, the sample shown in FIG. 1F (which cannot be measured by aconventional technique) can be measured with a reproducible error of 0.5nm. In addition, since the processed layer TL is not etched in the stateshown in FIG. 1F, it is easy to reproduce the sample by re-performingthe manufacturing process from the exposure process.

Fifth Embodiment

FIG. 8 is a flowchart showing a measurement according to a fifthembodiment of the present invention. After patterns are classified intogroups, a relative positional relationship between the groups isdetected in step 801. This is different from the other embodiments. Therelative positional relationship between the groups means the amount ofa superposition error between a pattern subjected to an exposure and apattern subjected to another exposure. More specifically, the relativepositional relationship (positional error) in an X direction is obtainedby using the center of the contour (extending in a Y direction) of thepattern as a reference, while the relative positional relationship(positional error) in a Y direction is obtained by using the center ofthe contour (extending in an X direction) of the pattern as a reference.The superposition error between the pattern subjected to the exposureand pattern subjected to the other exposure is very important in orderto measure the length of a space between the pattern portions, and thesize of a portion of the pattern subjected to a multi-exposure. Sincethis method is not carried out in conventional techniques, it isnecessary that the apparatus automatically classify the patterns intogroups.

In the present embodiment, after the patterns are classified based onthe brightness, and the contour of each pattern is obtained, thesuperposition error is obtained. When the superposition error is large,the exposure process is re-performed. This contributes to improvement inthe yield of semiconductors.

In the embodiments of the present invention, a scanning electronmicroscope using an electron beam is described as an example. The basicconcept of the present invention is not limited to this. Anothermicroscope using a charged particle beam such as an ion beam can beapplied to the present invention.

According to the present invention, it is possible to measure, with highaccuracy, the sizes of portions (having shapes different from each otherin a vertical direction) of a pattern on a sample subjected to amulti-exposure and a relative positional relationship between groups.Furthermore, it is possible to smoothly control a lithographic processand an etching process.

1. An electron beam measurement apparatus, which measures, based oninformation on an image, a pattern formed on a sample, comprising anelectron optical system that has a lens and a deflector and scans apredetermined observation region on the sample with an electron beamemitted from an electron source, a detector for detecting a chargedparticle secondarily generated from the sample by irradiation with theelectron beam, and means for forming an image based on the detectedcharged particle, the patterns being delineated in a single layerpresent on a substrate by a multi-exposure method, the electron beammeasurement apparatus including: means for classifying patterns, whichare included in an image acquired by the irradiation with the electronbeam on the patterns on the sample, into groups according to an exposurehistory record, the exposure history record being acquired based onbrightness of the patterns included in the image and a differencebetween shapes of white bands of the patterns.
 2. The electron beammeasurement apparatus according to claim 1, wherein the patterns areclassified into the groups based on an image formed based on a secondaryelectron of the charged particle and an image formed based on areflective electron of the charged particle.
 3. The electron beammeasurement apparatus according to claim 1, wherein the patterns areclassified into the groups according to the exposure history record bycomparing the acquired image with a design database.
 4. The electronbeam measurement apparatus according to claim 1, wherein the patternsare classified into the groups such that a pattern having portionarranged alternately is included in one of the groups that is differentfrom the other group including the other pattern.
 5. The electron beammeasurement apparatus according to claim 1, wherein an image processingparameter or an waveform processing parameter is used for each of theclassified groups to obtain the size of a portion of the patternincluded in the group or the position of the contour of the portion ofthe pattern, the used parameter varying depending on the group.
 6. Theelectron beam measurement apparatus according to claim 1, wherein areference image or a reference waveform is used for each of theclassified groups to obtain the size of a portion of the patternincluded in the group or the position of the contour of the portion ofthe pattern, the used reference image or the used reference waveformvarying depending on the group.
 7. The electron beam measurementapparatus according to claim 1, wherein information on a relativepositional relationship between the classified groups is obtained.
 8. Anelectron beam measurement apparatus, which measures, based oninformation on an image, a pattern formed on a sample, comprising anelectron optical system that has a lens and a deflector and scans apredetermined observation region on a sample with an electron beamemitted from an electron source, a detector for detecting a chargedparticle secondarily generated from the sample by irradiation with theelectron beam, and means for forming an image based on the detectedcharged particle, the patterns being delineated in a single layerpresent on a substrate by a multi-exposure method, the electron beammeasurement apparatus including: means for classifying the patterns inthe plurality of images into a plurality of groups according to anexposure history record by irradiating patterns with the electron beamto acquire a plurality of images respectively indicating regions thatmostly overlap each other under respective image acquisition conditionsdifferent from each other, wherein any of the images that is acquiredunder any of the image acquisition conditions is used for any of thegroups to obtain the size of a portion of the pattern included in thegroup or the position of the contour of the portion of the pattern, theimage acquisition condition varying depending on the group.
 9. Theelectron beam measurement apparatus according to claim 1, wherein thepatterns are delineated on the sample by a double patterning technique.10. The electron beam measurement apparatus according to claim 1,wherein the image formed based on the detected charged particle is ascanning electron microscope image.
 11. The electron beam measurementapparatus according to claim 8, wherein the patterns are delineated onthe sample by a double patterning technique.
 12. The electron beammeasurement apparatus according to claim 8, wherein the image formedbased on the detected charged particle is a scanning electron microscopeimage.